I deal with audio a lot due to my hobbies and where I work.
To directly answer your question, you should get an external DAC (Digital Audio Converter) and headphone amp. This will reduce electromagnetic interference coming from your PC, which internal sound cards that have dedicated headphone amps can suffer from.
now to supply with more information,
DAC's and amps can come as separate units or in a sort of all-in-one unit. Either would be fine for your situation, you just have to find one that suits your needs. I will not recommend any right now, as I do not know what kind of budget you have, nor do I know your needs outside of it being able to run your headphones.
I hope you find this information helpful